1. Field of the Invention
The present invention relates to a print head of an ink jet printer and a fabrication method thereof, and more particularly, to a bubble-ink jet print head and a fabrication method thereof, having an ink supply opening which improves the uniformity of the ink injection characteristics of respective injection nozzles, thereby assuring that the amounts of ink supplied to or jetted through respective injection nozzles even though the injection nozzles are highly integrated.
2. Description of the Related Art
Since an ink-jet printer is excellent in prevention of noise and in obtaining a high resolution and it is also capable of performing a color printing at a low cost, a consumer's demand for the ink jet printer has been increased.
Also, with the development of the semiconductor technology, print head fabrication technology, which is a main component of the ink jet printer, has been actively developed for the past decade. As a result, a print head having about 500 to 1,000 injection nozzles and capable of providing a resolution of 1200 dpi is currently being used in disposable ink cartridges.
FIG. 1 schematically shows a conventional print head 10 for an ink jet printer.
Generally, ink is supplied from a back surface of a substrate 1 of the print head 10 to a front surface of the substrate 1 through a first ink supply channel 2 composing an ink supply opening connected with an ink cartridge (not shown).
The ink supplied through the first ink supply channel 2 flows along restrictors or second ink supply channels 3 defined by a chamber plate 8 and a nozzle plate 9 to reach ink chambers 4. The ink temporarily stagnating in the ink chambers 4 is instantly boiled by a heat generated from heaters 6 disposed under a protective layer 5.
As a result, the ink generates an explosive bubble and, due to the bubble, some of the ink in the ink chambers 4 is discharged outwardly from the print head 10 through injection nozzles 7 formed above the ink chambers 4.
In such a print head 10, shape and disposition of the first and second ink supply channels 2, 3 and the ink chambers 4 are important factors that affect an ink flow and a frequency characteristic of unit nozzle.
For example, as shown in FIGS. 2 and 3, the frequency characteristic of unit nozzle is greatly influenced by a distance SH from the first ink supply channel 2 to inlets of the ink chambers 4 or connecting portions 4′ between the adjacent ink chambers 4.
More specifically, the smaller the width of the second ink supply channels 3 is formed, i.e., the closer the edge of the first ink supply channel 2 is positioned to the ink chambers 4, the better the ink supply performance of the injection nozzles 4 is, and thereby the frequency characteristic of unit nozzle can be improved.
Also, when fabricating a print head having above 500 injection nozzles 7, in order to obtain a superior scattering characteristic in ink jetting, the print head 10 should be fabricated to ensure that the distance SH from the first ink supply channel 2 to the respective ink chambers 4 is uniformly maintained.
Accordingly, the shape and disposition of the first and second ink supply channels 2, 3 and the ink chambers 4 are designed to ensure that the distance SH from the first ink supply channel 2 to the respective ink chambers 4 is uniformly maintained.
In the print head 10, the first ink supply channel 2 is generally is formed by etching the substrate 1 from the back surface to the front surface thereof through a wet or dry etching process, before or after forming the chamber plate 8 and the nozzle plate 9 or an one body chamber/nozzle plate (not shown) over the substrate 1 having the heaters 6 and switching elements such as transistors formed thereover.
However, the related art is not without problems. For example, if the first ink supply channel 2 is formed by a wet etching process of using a strong alkaline etch resolution such as Tetra-methyl-ammonium Hydroxide (TMAH), it requires that the front and the back surfaces of the substrate 1, except for a portion to form the first ink supply channel 2, should be masked by a layer of anti-undercut material and oxide or nitride having a high etch selectivity ratio to the strong alkaline etching resolution before performing the wet etching process, and removed the masking material to ensure that remnants thereof do not remain along the first ink supply channel 2 after performing the wet etching process.
Further, if the first ink supply channel 2 is formed by a dry etching process of using a sandblaster, it is possible that the edge of the first ink supply channel 2 is not only uncleanly formed as shown in FIG. 4, but also the heaters 6 and the switching elements are contaminated due to particles generated during sandblasting.
Also, if the first ink supply channel 2 is formed by a silicon dry etching process using an etch gas, since a protective layer 5 such as oxide or nitride having a high etch selectivity ratio to the etch gas is used as an etch stop layer over the front surface of the substrate 1, as shown in FIGS. 5A and 5B, lateral etching is generated due to charging phenomenon at the interface between the protective layer 5 and the substrate 1 thereby to unevenly form notches 2′ which are remained even after the protective layer 5 is etched and removed, so that first ink supply channel 2 is not regulated in a precise measure.
When the notches 2′ are unevenly formed as explained above, the flow of ink supplied to the injection nozzles 7 via the second ink supply channels 3 and the ink chambers 4 through the first ink supply channel 2 becomes uneven, thereby resulting in a non-homogenous frequency characteristic of unit nozzle.